Boneyard Library

As Boneyard Library enters the battlefield, you may exile a creature or sorcery card from your graveyard. If you don't, Boneyard Library enters the battlefield tapped.
{t}: Add {u} or {b} to your mana pool.
When not serving or scheming against her master Silumgar, Sidisi resides in an ancient library, seized from the Ojutai centuries ago.